Process for the desulfurization of petroleum oil stocks

ABSTRACT

LOW SULFUR-CONTENT PETROLEUM OIL STOCKS ARE PREPARED BY CONTACTING A SULFUR-CONTAINING OIL STOCK WITH AN ALKALI METAL, PREFERABLY SODIUM, OR AN ALKALI METAL ALLOY, PREFERABLY SODIUM/LEAD, TO PRODUCE A MIXTURE COMPRISING A LOW SULFUR OIL AND A MIXTURE OF ALKALI METAL SALTS DISPERSED THEREIN. THE MIXTURE OF SALTS IN OIL IS RESOLVED BY CONTACTING THE SAME WITH, PREFERABLY, 30-160 MOLE PERCENT HYDROGEN SULFIDE BASED ON TOTAL MOLES OF SALT IN THE OIL, A TEMPERATURE OF ABOUT 670* F. OR ABOVE WHEREUPON A SALT PHASE SEPARATES FROM THE OIL. THUS SEPARATED THE SALT IS BLENDED WITH A MOLTEN SULFUR-RICH ALKALI METAL POLYSULFIDE THEREBY FORMING A SULFUR-DEPLETED ALKALI METAL POLYSULFIDE AND LIBERATING HYDROGEN SULFIDE. IN ANOTHER EMBODIMENT OF THE INVENTION. MOLTEN SULFUR MAY BE USED IN PLACE OF THE POLYSULFIDE. THE SULFUR-DEPLETED POLYSULFIDE IS THEN DECOMPOSED ELECTROLYTICALLY TO REFORM ALKALI METAL AND A SULFUR-RICH POLYSULFIDE, FROM WHICH ELEMENTAL SULFUR IS RECOVERED.

' Jan.. 29, 1974 R, 'BE/mom JR, UAL 3,788,978

PROCESS FOR THE DESULFURIZATION OF PETROLEUM OIL STOCKS Jan; 29, 1974 R.BE,\RDE|\1,JR ETAL 3,788,978

PROCESS FOR THE DESULFURIZATION OF PETROLEUM OIL STOCKS Filed May 24,1972 3 Sheets-Sheet 2 1m29, 1914 RjB-EARDEN, JR., am 3,788,978

PROCESS FOR THE DESULFURIZATION OF PETROLEUM OIL STOCKS T76 l FIGURE 5lUnited States Patent O U.S. Cl. 208-208 M 23 Claims ABSTRACT OF THEDISCLOSURE Low sulfur-content petroleum oil stocks are prepared bycontacting a sulfur-containing oil stock with an alkali metal,preferably sodium, or an alkali metal alloy, preferably sodium/lead, toproduce a mixture comprising a low sulfur oil and a mixture of alkalimetal salts dispersed therein. The mixture of salts in oil is resolvedby contacting the same with, preferably, 30-160 mole percent hydrogensulfide based on total moles of salt in the oil, at a temperature ofabout 670 F. or above whereupon a salt phase separates from the oil.Thus separated the salt is blended with a molten sulfur-rich alkalimetal polysulfide thereby forming a sulfur-depleted alkali metalpolysulfide and liberating hydrogen sulfide. In another embodiment ofthe invention, molten sulfur may be used in place of the polysulfide.The sulfur-depleted polysulfide is then decomposed electrolytically toreform alkali metal and a sulfur-rich polysulfide, from which elementalsulfur is recovered.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to a process for the desulfurization of sulfur-containingpetroleum oil stock. More particularly, the process comprises contactinga sulfur-containing oil stock with an alkali metal or alkali metalalloy.

Description of the prior art In the last several years there has been anever-increasing concern about air pollu-tion. Some of the objects ofthis concern have been the discharge of sulfur oxides to the atmosphereupon burning sulfur-containing fuels. Over a period of many yearsseveral studies have been conducted with the object of developingefficient and economcal means for reducing the sulfur content of crudepetroleum oils and other virgin hydrocarbon fractions.

To the present, the most practical desulfurization process has beenhydrogenation of sulfur-containing oils at elevated pressures andtemperatures in the presence of an appropriate catalyst. The processrequires the use of hydrogen pressures ranging from about 200 to about2500 p.s.i.g. and temperatures ranging from about 650 to about 800 F.,depending on the nature of the oil to be desulfurized and the amount ofsulfur required to be removed.

The process is efficient in the case of distillate oil feedstocks andless efficient when used with those containing undistilled oil such aswhole crudes or residua. This is due to several factors. First, most ofthe sulfur in the oils is contained in high molecular weight molecules,and it is difficult for them to diffuse through the catalyst pores tothe catalyst surface. Furthermore, once at the surface, it is difficultfor the sulfur atoms contained in the molecules to see the catalystsurface. Additionally, the feedstocks may contain large amounts ofasphaltenes which tend to form coke deposits under the processconditions on the catalyst surface thereby deactivating the catalyst.Moreover, high boiling organometallic compounds pres- 3,788,978 PatentedJan. 29 1974 ICC ent in such stocks decompose and deposit metals on thecatalyst surface thereby diminishing the catalyst life time. The severeoperating conditions employed in the process cause appreciable crackingof high boiling oils thereby producing olefinic fragments which,themselves, consume hydrogen, thereby lowering the process efficiencyand increasing costs.

Alternate desulfurization processes that have been ernployed in the pastused alkali metal dispersions, such as sodium, as desulfurizationagents. Bascially, the process involved contacting a hydrocarbonfraction with the sodium dispersion, the sodium reacting with the sulfurto form dispersed sodium sulfide (NagS). However, such a process was notproven to be economically advantageous, particularly for treatment ofhigh boiling, high sulfur content feedstocks due to (a) the high cost ofsodium, (b) problems related to removal of sodium sulfide formed in theprocess from the oil and (c) the impracticability heretofore ofregenerating sodium from the sodium sullide.

In theory, it has been determined that the best approach to this problemof sodium regeneration would be to electrolyze an alkali metal salt thatmelts at about the same temperature as used for the desulfurizationprocess and which can be electrolyzed with minimum consumption ofelectrical energy. The alkali polysulfides, preferably the sodiumpolysulfides meet this requirement. There are three sodium polysulfideswith melting points as follows: N212S2 (885 F.), Nil-S4 (545 F.) andNa2|S5 (485 F.). These polysulfides are mutually soluble andintermediate compositions, having intermediate properties, can form. Theeutectic is at about Na2S31 with a melting point of about 450 F.Moreover, the electrolysis of molten sodium polysulfide consumes lesselectrical energy than electrolyzing molten sodium chloride, thetraditional electrolysis salt.

The cost of sodium as a reagent used on a oncethrough basis isprohibitively high, and it is therefore clear that one must be able torecover the sodium from the sodium sulfide in order to provide aneconomically viable process. Much thought has been given to this problemin the past, but until now no economical process has been developed. Oneof the major difficulties has been the separation of the sodium sulfidefrom the oil.

SUMMARY OF THE INVENTION In accordance with this invention, it has nowbeen discovered that an economically feasible desulfurization processVis-a-vis hydrodesulfurization of whole crude or residual oils can beachieved and that outstanding sulfur removal can be realized.Specifically, the process involves contacting a sulfur-containingpetroleum oil stock with a desulfurization agent comprising an alkalimetal, such as lithium, sodium, potassium, and the like, preferablysodium, or an alkali metal alloy, preferably sodium/lead, atdesulfurization conditions, thereby forming a mixture comprising an oilof diminished sulfur content containing alkali metal salts andcontacting at least a portion of said mixture with I-I2S.

The alkali metal salts comprise in addition to alkali metal sulfide,by-product alkali metal salts such as organo metal salts, metal oxides,mercaptides, amides and the like. Hereinafter the invention will bedescribed with respect to sodium although it is understood that otheralkali metals as hereinbefore disclosed may be used.

In a preconditioning step for salt recovery at least a portion of theoil-salt mixture (generally in the form of a dispersion of submicronsodium salts in oil) is contacted with HZS in amounts ranging from about10 to about mole percent, based on the total number of moles of saltpresent in the mixture, preferably 30 to 60 mole percent. The netconsequence of the HZS treatment is twofold: (1) at least a portion ofthe by-produet sodium salts such as sodium oxide, sodium hydroxide andthe like are converted to sodium hydrosulde, and (2) submicron salts areagglomerated to yield a macrocrystalline salt phase (preferebaly havinga particle size between about 150 and 200 microns) which readilydisengages from the oil phase. The salt phase is separated from the oilphase and recovered employing one of several well known commercialtechniques, notably filtration or centrifugation. The B2S-treatedmixture of salts is then contacted with a sulfur-rich sodium polysulide,desirably in the molten state and preferably represented by the formula,NazSX (where x varies from about 4.0 to 4.9, preferably from about 4.4to 4.8, most preferably from about 4.5 to 4.7). The contacting resultsin the formation of a sulfur-depleted sodium polysulide, `i.e., Na2Sy(where y ranges from about 2.8 to 4.5, preferably from about 3.5 to 4.3,most preferably from about 4.0 to 4.2), desirably at a temperature abovethe melting point of the resulting polysulde. This recovery andconversion method will be hereinafter referred to as Scheme A.

Alternatively, the H2S-treated mixture of salts in oil i.e., withoutsalt separation from the oil, can be contacted directly with the moltenpolysulde (Na2SX) thereby converting at least a portion of the salts insitu to a sulfur-depleted polysulfde, NazSy, which is preferably in amolten state (Scheme B). It is preferable that the value of y in thesulfur-depleted polysulde NazSy be in the range of about 2.8 to 3.5 inorder to avoid backsuliding of the oil phase by the polysulde.

The Na2Sy is subsequently electrolyzed in an electrolytic cell as morefully described below, and sodium is withdrawn therefrom and eitheralloyed with a molten metal such as lead or tin or introduced directlyinto the desulfurization zone in undiluted form.

In a second embodiment of the invention (Scheme C) an excess amount ofHES is added to the sodium sulfide/ oil mixture thereby converting thesodium sulide (and other sodium salts present therein) to sodiumhydrosulfide (NaSH). The amount of hydrogen sulde added can range fromabout 110 mole percent based on the total number of moles of saltpresent in the oil up to about 400 mole percent, but is preferably usedin amounts ranging from about 120 to 160 mole percent. At the contactingtemperature employed, the NaSH is substantially molten and is readilyseparable from the oil. Thereafter, the NaSH is contacted with eitherNazStx or sulfur to form NazSy which is electrolyzed to form sodium.

It is also possible, and, perhaps desirable, to convert NaSH to NazSiyby contact with molten sulfur rather than the molten polysuliide NaZSX.According to this procedure, (Scheme D), molten sulfur obtained frompyrolysis of the electrolysis product, NazSz, is added to the oil-free,molten NaSH stream. Normally, suflicient sulfur is added to give thedesired electrolysis feed, i.e., NazSy, Where y ranges from about 3.5 to4.3.

It should be noted that in each of the foregoing schemes for therecovery and conversion of desulfurization salts, that hydrogen sulfideis liberated when the H2S-treated salts are contacted with sulfur-richsodium polysulde or elemental sulfur. 'Ihe hydrogen sulfide isrecovered, puried to remove traces of water and recycled in the process.

The amount of Na2Sx that is required to react with the HzS-treated saltmixture varies and is dependent on the compositions of both thesulfur-rich polysulfide and the sulfur-depleted polysulfide. Thereaction of Na2Sx with either NazS or NaSH is thought to proceed asfollows:

From the above stoichiometry, it is seen that the same amount of NMS,zis required to react with 2 moles NaSH 4 as with 1 mole Na2S to yieldthe same quantity of NagSy. The values of n and m in the above equationswill depend on the values chosen for x and y. Using the equations, theamount of Na2Sx required to react with a salt mixture comprising l moleof Na-ZS, i.e., n and 1 mole of NaSH,

Le., nl' 1S:

Moles NazSx to react with y-l l mole of NazS (n) az-y (3) Moles NazS,lto react Wit.h y (y-l 1 mole of NaSH (m) 2 x-y (4) where:

y=the number of sulfur atoms in Nagsy .uzthe number of sulfur atoms inNaZSx Knowing the number of moles of NazS and NaSH present in the saltmixture and the values for x and y, the required amount of Nazx can bedetermined. It is noted that the calculated amounts of Na2Sx are minimumvalues and that larger quantities may be required depending on theamount of other salts that may be present in the salt mixture which alsoreact with th NaZSx.

Any feedstock from which sulfur is desired to be removed may in theorybe used in the instant process. Thus, for example, suitable feedstocksinclude whole crude such as Safaniya crude (Middle East), Lagunillascrude (Venezuelan), or U.S. crudes, residual fractions or any distillatefraction. The subjectprocess is particularly adapted to thedesulfurization of whole crude or residua that are difficult to treat byother methods such as hydrodesulfurization. While the feedstock may befed directly to the initial contacting zone for desulfurization withoutpretreatment, it is desirable to desalt the feed in order to preventNaCl contamination of the molten polysulide feed to the electrolysiscell. Desalting is a well-established process in the industry. Aparticularly preferred desalting process involves the addition of asmall amount of water to the oil in order to dissolve the salt containedtherein, followed by electrical coalescers. The oil is then dehydratedbyconventional means known in the industry.

The sodium may be used as a dispersion of the pure metal or in the formof a Amolten alloy such as sodium/ lead or sodium/tin. When sodium/leadis the alloy, desirable proportions comprise about 0.3 to about 0.5g.-atom sodium/0.7 to about 0.5 g.atorn lead, and when using sodium/tin,about 0.2 to 0.3 g.atom sodium/ 0.8 to 0.7 g.atom tin.

The contacting of the sodium metal or sodium metal alloy with thesulfur-containing oil is preferably carried out at temperatures andpressures suicient to maintain the bulk of the reactants within thereaction zone in the liquid phase. However, conditions may be varied toprovide vapor phase contact. The reaction temperature will generally bemaintained between about 450 and 750 F., preferably 600 to 700 F. Thereaction pressure will depend on the feed and temperature employed. Forreduced crude fractions the pressure will range between about 10 andp.s.i.g., preferably 40 to 60 p.s.i.g. For whole or topped crude,pressures may be raised to as high as about 500 to 600 p.s.i.g. in orderto maintain all or most of the oil in the liquid phase.

The sodium metal reacts with the sulfur-containing oil stock as shown inEquation 5 below to yield sodium sulfide which generally forms as amicrocrystalline dispersion in the oil.

In addition, organo-oxygen contained in the feedstock is removedtherefrom by reacting with the sodium metal. Furthermore, depending onthe amount of trace water present in the feed and the reactionconditions, varying amounts of thiosulfate, hydroxide and salts oforganic acids may be formed. (Typical crudes contain between about 0.1and 0.2% organic oxygen). Additionally, some organo-nitrogen andorgano-metals are also removed from the oil by reaction with the sodium.

The desulfurization step is conducted as a batch or continuous typeoperation but is preferably continuous. In general, the various meanscustomarily employed in extraction processes to increase the contactarea between the oil stock and the sodium metal or alloy thereof can beemployed. The apparatus used in the desulfurization step is of aconventional nature and can comprise a single reactor or mutiplereactors equipped with (a) shed rows or other stationary devices toencourage contacting; (b) orice mixers; (c) eicient stirring devicessuch as mechanical agitators, jets of restricted internal diameter,turbomxers and the like, or (d) a packed bed. The petroleum oil stockand the sodium metal or sodium metal alloy can be passed through one ormore reactors in concurrent, crosscurrent, or countercurrent ow, etc. Itis preferable that oxygen and water be excluded from the reaction zones;therefore, the reaction system is thoroughly purged with dry nitrogenand the feedstock dried prior to introduction into the reaction. It isunderstood that trace amounts of water, i.e., less than about 0.5 weightpercent, preferably less than about 0.1 weight percent based on totalfeed, can be present in the reactor. Where there are larger amounts ofwater, process eiciency will `be lowered somewhat as a consequence ofsodium reacting with the water.

The resulting oil dispersion is subsequently removed from thedesulfurization zone and contacted with HZS as described supra.Treatment of the HZS-treated salt mixture according to any of SchemesA-D, results in the formation of a sulfur-depleted sodium polysuliide,i.e., Nagsy.

After further treatment of the Na2Sy to remove various impuritiespresent therein, the NazSy is cycled to electrolytic cells wherein it isdissociated to form molten sodium and a sulfur-rich sodium polysulde,i.e., Na2Sz wherein z ranges from about 4.5 to 5.0, preferably fromabout 4.6 to 4.9, most preferably from about 4.7 to 4.9. The sodiumthereby formed is then withdrawn and either alloyed with a molten metalsuch as lead or tin or introduced directly into the desulfurization zonein undiluted form as hereinabove described.

The electrolytic cell unit will preferably comprise a sodiumion-conducting physical and electronic barrier or membrane thatseparates alkali metal on the one side from alkali metal polysulde onthe other side. Generally, the membrane may be composed of any materialthat can function as a sodium ion-conducting separator; however,beta-alumina containing sodium oxide is preferred. Such beta-aluminawill contain sodium oxide in the general range of aboutNa20-11Al2O3-Na20'5Al2O3. It is noted that when an alkali metal otherthan sodium is employed in the instant process, the oxide of the alkalimetal will be admixed with the beta-alumina in lieu of NazO.

The beta-alumina may be used in the pure form of doped with a smallamount of metal oxide such as MgO, LizO and the like. A detaileddiscussion of doped betaalumina is provided in an article appearing inthe Electrochemical Society -Extended Abstracts-Los Angeles Meeting-May-15, 1970, entitled Ionic Conduction in Impurity Doped ,B-alumina, byAtsuo Imai et al., the disclosure of which is incorporated herein byreference. Reference is also made to U.S. Pats. 3,488,271 to J. T.Kummer et al. and 3,475,225 to G. T. Tennenhouse. During cell operation,sodium ions migrate from the sodium polysuliide side, i.e., the anodeside, through the barrier to the sodium metal side, i.e., the cathodeside, where they are neutralized by electrons. At the same timepolysulde ions give up their electrons at the electron-conducting anodeto form elemental sulfur that then reacts with additional polysultideanions to form new polysulde ions, i.e., Sz=, of greater sulfur content.

As indicated above, z will take values in the range of about 4.5 to 5.0.The Sz: anions are continually removed from the cell in combined formwith sodium, i.e., NagSz. The anode may comprise any suitable electronconducting-current collector such as graphite, molybdenum, titanium,chromium, stainless steel, or aluminum that can withstand corrosiveattack of the sodium polysulde. The cells are arranged preferably inseries electrically, so that the anode for one cell is the cathode forthe one adjacent to it. The overall reaction is shown below:

cathode side anode side The recovered Na2SZ can be reduced in sulfurcontent to Na2SX (the latter being contacted with the H2S-treated saltmixture as described supra) by application of a vacuum and/or heatthereby liberating sulfur corresponding to that which was removed fromthe oil. Alternatively, at least a portion of the Na2SZ may be contacteddirectly with the HzS-treated salt mixture.

In other embodiments, elemental sulfur is allowed to build up in thecell and the operating temperature therein is maintained high enough sothat the sulfur is continuously removed therefrom as vapor. In anotherembodiment liquid sulfur forms in the cell and is separated from thepolysulde outside the cell. In yet another embodiment liquid sulfurforms in the cells and is separated from i.e., in situ, before themolten sodium metal is withdrawn from the electrolytic cell bycontinuously feeding lead or spent sodium/ lead alloy to the cathodeside of the cell.

While a beta-alumina type cell has been described, any other cell thatis capable of economically decomposing sodium polysulde into moltensodium is sufficient for the present purposes. A particular beta-aluminaelectrolytic cell and methods for the preparation of beta-alumina aredescribed in such patents as U.S. 3,488,271 and 3,404,036 to J. T.Kummer et al., U.S. 3,468,709' to J. T. Kummer and U.S. 3,446,677 andU.S. 375,225 to G. T. Tennenhouse, the disclosures of which areincorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ow diagram of the overalldesulfurization process using sodium metal in pure form. Desulfurizagonsalts are recovered from the oil according to Scheme FIG. 2 shows thereactor system for desulfurization with an alloy of sodium, i.e.,sodium/lead.

FIG. 3 shows the changes required to operate the process using saltrecovery Scheme B.

FIG. 4 shows the steps used in salt recovery Schemes C and D.

FIG. 5 is a simplified scheme showing the formation of the molten sodiumwithin the electrolyte cell.

Referring to the drawings in detail, the desulfurization reactor systemsused in the instant process vary depending on whether sodium or sodiumalloy is used as the reactant. The system using sodium will be describedrst, then the system using sodium alloy.

Turning now to FIG. 1 and the description of Scheme A, asulfur-containing feedstock, preheated to 450500 F., is fed by means ofline 1 and pump 2 to separator vessel 3 where trace amounts of water andlight hydrocarbon fractions are removed through line 4. The feed is thendischarged through line 5 by pump 6 to lter vessel 7 wherein particulatematter, i.e., coke, scale, etc., is removed.

The feed is preliminarily desalted by conventional means (not shown).Feed exiting the iilter via line 8 is split into two streams. A smallportion is fed through line 9 and heat exchanger 14 to dispersatorvessel 11 where a dispersion is formed with sodium entering through line67. The dispersator vessel is of a conventional design and is operatedat Z50-300 F. at atmospheric pressure. The vessel is blanketed withnitrogen. The resultant dispersion, drawn thorugh line 12, blends withthe balance of the feed in line 10 and enters the `charging pump 13,Where the pressure is raised to about 500 p.s.i.g., for whole crudes anddistillates and about 50 p.s.i.g. for residual fuels. The feedstock willordinarily be a whole crude of about 1 to about 3 weight percent sulfurbased on total feed or a residual stock of about 2 to about 7 weightpercent sulfur based on total feed, although distillate stocks can beused.

The oil enters heat exchanger 16 via line 15 where the temperature israised to about 00 to 550 F. and is then fed through line 17 to reactorvessel 18. The reactor contains bafiies 19 to promote continuing contactbetween sodium and the oil and to prevent bypassing from the inlet tothe outlet. Holding time in the reactor is about 15 to 60 minutes and ispreferably 30 minutes. The temperature at thertop of reactor 18 is about680 F. Gas that is formed due to the increase in temperature is takenoverhead through line 20 and is condensed and depresf surized byconventional means (not shown). The desulfurized oil containingdispersed sodium sulfide and other salts leaves the top of reactor 18via line 21.

The remainder of FIG. 1 will be explained below after describing thealternate reactor system for sodium alloy shown in FIG. 2.

FIG. 2 shows the reactor system for the case where sodium alloy is used.It differs from the case where sodium alone is used primarily in thatoil is recycled to the reactor in order to prevent cooling of the alloybelow its melting point and in order to recover and recycle the spentalloy. The feedstock which has been preliminarily preheated, dehydratedand de salted as per FIG. 1 is premixed in line 17 with desulfurizedrecycled oil from pump 68. The mixed oil stream enters reactor vessel 69via line 17 and flows in an upward direction therethrough. The vessel isof such a size that the oil remains in the reaction portion below thesodium alloy disperser 70 for about minutes to about l hour. The sodiumalloy, preferably sodium/lead or sodium/ tin or a mixture of the two,enters reactor 69 via disperser 70. Atom compositions of about 0.3 to0.5 Nat/0.7 to 0.5 Pb or 0.2 to 0.3 Na/ 0.8 to 0.7 Sn are suitable.

The alloy droplets commingle with the rising oil stream and beingheavier than the oil and of large enough size, fall downwardly throughthe rising oil stream. Baffles 71 promote contact. The spent alloycollects in the bottom of reactor 69 and passes via line 72 to the alloystorage vessel 73. The alloy is fortified by contact with freshlyregenerated sodium entering vessel 73 via line 67. Pump 75 feeds thefortified alloy via line 76 to disperser 70.

The dispersed oil passes into a settler zone located in the top ofreactor 69 where any small, entrained alloy particles are allowed tosettle. Bafes 77 act as collecting plates for the alloy particles andare placed at a slight angle so that the coalesced alloy can run off theends. The desulfurized oil/sodium sulfide dispersion leaves reactor 69via line 21.

One particular reactor system has been described. However, the alloy andoil can ow concurrently, and any one of several well-known types ofmixers such as pump mixers, high shear mixers or paddle blade mixers andthe like can be employed. Other settling means, in particular external,long, horizontal ow vessels or liquid cyclones and the like can be alsoused.

'Sodium sulfide-oil dispersion in line 21 is introduced into contactingvessel 22 wherein the said dispersion is contacted with 30-80 molepercent hydrogen sulfide based on the total moles of salts contained inthe oil, at a ternperature between about 60G-800 lF., preferably 625-750 F., eg., 700 F., and most preferably at the temperature of thedesulfurizaiton step. The pressure is maintained between about 25-50p.s.i.g. Hydrogen sulfide is introduced into said contactor via line 23.Residence time in the contactor vessel is on the order of about 10minutes, although longer or shorter times may be used if desired.

The H2S-treated dispersion exits through line 24 at about 700 F., and25-100 p.s.i.g. and is then cooled to about 450 F. in heat exchanger 25.The mixture is then fed through line 26 to hydroclone vessels 27 and 28in series. Desulfurized oil is withdrawn via line 29 to heat exchanger30 and exits at Z50-300 F. through line 31. An acid, such as dilutesulfuric acid or acetic acid, may be injected into line 31 through line32 to react with oil soluble sodium salts, eg., sodium mercaptides andthe like and the resultant mixture enters the electrostatic precipitator34 via line 33. The acidic aqueous phase from vessel 34 is withdrawnthrough line 36 and discarded. Desulfurized oil is fed through line 35to steam stripper 37 and subsequently to storage via line 38.

Oil-salt slurry drawn from the hydroclone vessels through lines 39 and40 is fed to wash vessel 41 where a light hydrocarbon Wash, enteringthrough line 42, is used to remove heavy adhering oil. The wash eluentis drawn off through line 43 and is eventually fractionated to recoverthe desulfurized oil content and the light hydrocarbon. The wash vesseloperates at 25-100 p.s.i.g. at temperatures of 150-300" F. A slurry ofwashed solids is fed through line 44 to drier 45 to remove lighthydrocarbon, which is taken off through line 46.

Dry solids are fed to blending vessel 48 via line 47, wherein contact ismade with sulfur rich polysulde (Nazsx as hereinabove described) thatenters the vessel through line 49. The contacting is conducted at atemperature of about 500 to 820 F., preferably 600800 F., mostpreferably from about 650-750 F., e.g., 700 F., and at a pressurebetween about atmospheric pressure and p.s.i.g., preferably betweenatmospheric pressure and 50 p.s.i.g. Hydrogen sulfide released in theblending reaction along with some small amount of light hydrocarbon isremoved through line 50, blended with makeup hydrogen sulfide enteringfrom line 51 and is recycled to vessel 22 by way of line 23.

The molten sulfur depleted polysulfide (Na2Sy as hereinabove defined)formed by the reaction of H2S-treated salts with sulfur-richpolysullfide is removed from blending vessel 48 through line 52 and fedto iilter vessel 53 to remove particulate matter such as coke and meltinsoluble salts. 'Line 54 is used to purge a small stream of sodiumpolysullide `from the system in order to prevent buildup of impuritiesto an inoperable level.

These dissolved impurities arise from the feed and from equipmentcorrosion as well as from the organometallic compositions removed fromthe feed by the action of sodium. Specifically, compounds containingcombined iron., vanadium, silica, nickel, chromium, lead and tin mayform and are removed from the system via line 54.

In addition to the above-mentioned impurities, Na2CO3, Na2SO3 and thelike may also be present in the polysulfide. With the exception ofNa2CO3 (which can be removed by Ca(OH)2 treatment), these impurities canbe removed by treatment with H28, thereby converting at least a portionof the impurities to polysulfide. Treated NazSy is introduced into cell56 via line 55.

The process incorporating salt recovery Scheme B is illustrated byreference to FIG. 3. The hydrogen sulfidetreated oil-salt dispersionremoved 'from contactor vessel 22 is fed through line 26 to scrubbingtower 80 wherein it is contacted countercurrently with molten sodiumpolysulfide (Na-28X) that is introduced via line 95.

The tower is divided into a series of stages by foraminous plates 81 andis maintained at a temperature ranging from about 500 to 800 F.,preferably 650 to 700 lF., and a pressure ranging from about 50 to 500p.s.i.g., preferably about 50 to about 100 p.s.i.g. The

9 sodium sulde dispersed in the oil reacts with the sodium polysulde toyield a molten sulfur-depleted polysullide (-Na2Sy wherein y varies from2.8 to 3.5), which drops from the oil and collects at the tower botton.If necessary, additional hydrogensulfide can be added to the meltthrough line 91 to effect conversion of by-product salts to the sodiumpolysulfide.

While the polysulde contacting step has been shown here to becontinuous, it may also be conducted as a batch operation. In general,the various means customarily employed in extraction processes toincrease the contact area between the various materials can be employed.The apparatus is of a conventional nature and can comprise a singlereactor or multiple reactors equippcd with eicient stirring devices suchas mechanical agitators, jet of restricted internal diameter,turbomixers and the like. The sodium polysulde, i.e., NaZSX and theoil/sodium sulfide mixture can be passed through one or more reactors inconcurrent, crosscurrent or countercurrent flow.

Excess hydrogen sulfide, hydrogen sulfide liberated in the NagSX-NaSHreaction and liberated water are removed from the reaction through line50. After suitable drying (not shown) the hydrogen sulfide stream isrecycled to the contactor vessel 22. As in the preceding case,desulfurized oil exits via line 29 for further processing and storage.

The molten sulfur-depleted polysulde (.NaZSy where y varies from 2.8 to3.5) removed from the tower via line 96 is split into two parts. Oneportion is fed through line 94 to blend with a portion of thesulfur-rich polysulfide product entering from line 93. The ratio ofsulfurrich and sulfur-depleted polysulide will be regulated by the valueof x in the desired scrubbing agent, NazSx. The remainingsulfur-depleted polysullide in line 97 is blended with the remainingsulfur-rich polysulfide entering from line 92 and the resultant mixtureis fed via line 52 to the electrolytic cells.

The process incorporating salt recovery Scheme C is illustrated byreference to FIG. 4. According to this scheme an excess amount (110-160mole percent based on total salts contained in the oil) of hydrogensulfide is added to the oil-salt dispersion in vessel 22 at aternperature of about 670'-800 F., preferably 680-750 F. and at apressure of about 50-500 p.s.i.g., preferably 100- 200 p.s.i.g. Theresultant mixture is then fed via line 26 to the settler vessel 82 whichoperates at conditions similar to those used in vessel 22. Residencetime is on the order of 5 to 30 minutes, preferably about 15 minutes.Molten sodium hydrosulde separates from the oil, collects at the bottomof the settler and is drawn off through line 83 which feeds directly tothe polysulde blending vessel 48 as noted in FIG. 1. Subsequent stepsare identical to those described in FIG. l. The product oil is withdrawnthrough line 29 and is processed according to Scheme A of FIG. l.

The process variation noted as Scheme D is illustrated in FIG. 4. Moltensodium hydrosulde is withdrawn from settler vessel 82 and fed via lines83 and 84 to blending vessel 86, where it is contacted with moltensulfur (line 85) at a temperature between about 500-800 F., preferablybetween 600 and 700 F. and at a pressure between atmospheric pressureand 100 p.s.ig., preferably between atmospheric pressure and 50p.s.i.g., rather than molten sodium polysulde, NazSX. The mole ratio ofsulfur to NaSI-I is maintained in the range of 1:1 up to 3:1 butpreferably at l.5 to 2.0.

The sodium polysulde product, i.e., Na2Sy Withdrawn through line 99, isyblended with pyrolyzer polysulde product (NazSX) and fed via line 52 tothe electrolytic cells. Liberated hydrogen sulfide is taken overheadthrough line 50 and is ultimately recycled to contacting vessel 22. Thepyrolyzer vessel 60 is operated at conditions rela- 10 tively moresevere than those used in Scheme A in order to furnish the volume ofsulfur required.

A dry nitrogen stream (not shown) blankets the electrolytic cells. Theelectrolytic cells may comprise any cell capable of converting thepolysuliide to sodium metal. Preferably, the individual cell unitcomprises a molten sodium-containing cavity and a molten sodiu-mpolysulfidecontaining cavity separated from each other by a sodiumion-permeable membrane comprising preferably crystalline beta-alumina asalready described.

A schematic representation of one embodiment of a cell unit is shown inFIG. 5. In operation, electrons ow through the metal separator sheet 1entering the molten sodium-containing cavity 2, wherein sodium cationscombine with the electrons and are reduced to elemental sodium that iswithdrawn from the cavity via line 3. The beta-alumina membrane 4 actsboth as a physical separator and alkali ion conductor between the twocavities. Sodium polysulfide is introduced into cavity 5 via line 6; itis, by its nature, highly ionized into sodium cations and polysuldeanions. The latter are oxidized to elemental sulfur that reacts furtherto yield sulfur-enriched polysulfide anions. The anions along with therequisite sodium cations are subsequently removed via line 7 from cavity5 as sulfur-enriched sodium polysulde (Na2Sz where z varies from about4.5 to 5.0). Electrons which are given up by the polysulde anions flowthrough the metal separating sheet (current collector) 8, which alsoserves as the anode to form a complete circuit. Thus the anode for onecell ybecomes the cathode for the next. The cell cavity 5 may bepartially or fully filled with a porous or nonporus electron-conductingmaterial such as graphite, molybdenum, titanium, chromium, aluminum,nickel-iron alloys and other alloys and the like.

As noted above, although beta-alumina is shown as the preferredseparator, any other separator that is sulicient for the purposes may beemployed. Additionally, an alternate embodiment comprises forming andcontinually removing elemental sulfur from the cell. In practice, theelectrolytic cell 56 comprises a plurality of individual cell units inorder to provide a sufcient output of sodium.

A plurality of cells, e.g., about -200 cells may be operated in seriesin order to build up the overall voltage to about 280-700 volts. Thetotal amount of cell area required depends on the amount of sodiumrequired, and is in the range of about 20 to 70 square feet per poundper minute of sodium. The temperature in the cell rises to about 700-820F., depending on the amount of cell area, current density used, theresistance of the cell elements and their condition.

The composition of the sodium polysuliide leaving the electrolytic cellcan be controlled by the ow rate and the current. The greater the owrate the less is the increase in sulfur content; the greater the currentthe greater is the mcrease in sulfur content. The composition iscontrolled such that by applying a reasonable vacuum (and/or heat 1fdesired), sulfur corresponding to that which was removed from the oilcan be taken overhead.

Accordingly, the sodium polysulde formed in the electrolytic cell ispassed via line 57 to surge vessel 58 and then to stripping vessel 60which is partially evacuated, e.g., to an absolute pressure of about l0to about 300 mm. Hg, preferably about 50 to 100 mm. Hg, to vaporize someof the sulfur and reduce the sulfur content of the polysulfide so thatthe final polysulde composition is Na-SX wherein x takes values rangingfrom about 4.0 t0 about 4.9, preferably about 4.4 to about 4.8. Atonetenth atmosphere sulfur vapor pressure, for example, the compositionin equilibrium therewith is approximately Na2s4 32 at 700 F., N32S473 at750 F., and Na2s4'64 at 800 F. The sulfur vapor is taken overheadthrough line 61 and condensed by conventional means (not shown). Asindicated supra the resulting polysulde is then recycled via line 49 toscrubbing tower 48. Alternatively, at least a 11 portion of the sodiumpolysulfide stream exiting from the cell can be contacted directly withthe HzS-treated salt mixture, thereby by-passing the evacuatingoperation in vessel 60. Thus, for example, Na2S5 exiting from the cellcan be contacted directly with the HZS-treated salt mixture. The moltensodium is subsequently removed from the electrolytic cell through acurrent breaker (not shown) and passed via line 62 to surge vessel 63where it is blended with makeup sodium entering at line 64 and then fedvia line 65, pump 66 and line 67 to vessel 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will bemore clearly understood by reference to the following examples:

Description of apparatus and procedures (A) Sodium treatment reaction:The reactor consisted of a standard, one liter Paar autoclave, which wasconstructed of Monel steel. Two modifications were made, however. Anoversized turbine blade stirrer head was substituted for the standarditem to aid in lifting and dispersing sodium and its alloys,particularly the alloy with lead. Also, the dipleg was tted with a 50micron metallic filter element to aid in sampling the oil phase whenmixtures of salts and oil were present. The reactor head contained theusual openings and fittings for measurement of pressure and temperatureand for the addition of gases.

In the typical run the reactor was charged at room temperature with thedesired quantity of sulfur-containing oil and freshly cut sodium.Alternatively, in some runs, S- dium was added as an alloy with lead.The reactor was sealed and thoroughly flushed with nitrogen. About 50p.s.i.g. of the flush gas was present when heatup was begun. The reactortemperature was brought to approximately 450 F. prior to beginningstirred cotact, thereby minimizing the reaction time below the normalrun temperaure range of 60G-700 F.

The yield of gaseous products, comprising materials lighter than or thesame weight as pentane was determined by cooling the reactor to roomtemperature, venting the gases through a wet test How meter to determinevolume and then submitting a representative sample for componentanalysis by mass spectrometry.

Coke formed in the desulfurization reaction was most often recoveredwith the sodium salts and is reported as the water insoluble fraction ofthe salt.

Without exception, the combined coke and C5* gas yield never amounted tomore than 1.0 wt. percent of the feed and usually was less than 0.5 wt.percent on feed. Therefore, coke and gas yields are not reported in theexamples which follow. Also, desulfurized oil recoveries wereessentially quantitative in all examples.

(B) Hydrogen sulde treatment preparatory to salt recovery: Hydrogensulfide, was added directly to the reactor mixture contained in thesodium-treating reactor. Normally, the addition was made immediately atthe end of the sodium treating step and at the same temperature employedin that step. A weighed amount of reagent was loaded into a 200 ml.stainless steel bomb which was then fitted to a reactor inlet valve.Hydrogen sulfide was injected under its own vapor pressure. The bomb,previously tared, was always reweighed after addition to determine theamount of reagent retained.

(C) Separation of the oil and salt phases: Again, the sodium-treatingreactor was used. After injection of hydrogen sulfide, stirring wasceased for a time suicient to allow the salt phase, eithermacrocrystalline solids or molten salts, to settle (the salts exhibit adensity roughly twice that of oil). If desired, oil samples could thenbe withdrawn through the filter-modified dipleg while still at theapproximate temperature of the sodium treating reaction. Ultimately,however, the reactor was cooled to about 200 F., opened and the bulk ofthe oil phase decanted. Precipitated salts were slurry washed withtoluene to remove adhering oil and then dried.

If the preparatory treatment was designed for generation of molten saltsthen the reactor was cooled to 200 F. without agitation. In this casethe salts formed a solid layer on the reactor bottom and were removedwtih hammer and chisel. The solidified molten layer was subsequentlycrushed, washed with hydrocarbon and dried.

Salt recovery via blending with molten sodium polysulfide (Na-28x)required cooling the reactor to 200 F., adding the polysulfide as apowder and heating again to the melting point of the polysulde endproduct. The molten salt recovery procedure was then used.

(D) Conversion of salts to sodium tetrasullide (NazSy) The reactor forthis step consisted of a three neck, 500 ml. roundbottom ask made ofPyrex glass. The reactor was tted with a stirrer, a temperatureindicator probe, a gas inlet tube and a screw feeder for adding powderedsolids.

Conversion of H2S-treated salts to sodium tetrasullide was accomplishedby melting the required amount of sodium pentasuliide (M.P.-485 F.) inthe reactor under an atmosphere of dry nitrogen. With the temperatureadjusted to 600 F. (above the melting point of endproduct salt),powdered B2S-treated salt was fed in by means of the screw feeder.Hydrogen suliide evolution was instantaneous. Gentle stirring was usedto break up solid crusts that formed on the surface from time to time.Upon completing the salt addition, the resultant melt was held for 15minutes at `600" F. to insure complete reaction. A lcontinuous nitrogensweep was employed to carry the evolved H28 to a sodium hydroxidescrubber. Upon completion of the heating period, the melt was cooled toroom temperature, pulverized and stored under nitrogen.

When small samples of the HzS-treated salts were converted (l0 g. orless), the salts were simply premixed with polysulde :and heated to 600F.

Sulfur can be substituted for the sodium pentasulde reactant, in whichcase the powdered sulfur and H2S- treated salts are premixed and thenheated to 600 F. Hydrogen sulfide evolution is rapid beginning at about400 F. and is complete by the time a homogeneous melt is obtained at 600F.

(E) Electrolysis of sodium tetrasulfide (NagSy) (sodiumregenerationproposed technique): The laboratory electrolytic cellconsists of a beta-alumina tube sealed into a Pyrex glass reservoir forsodium metal and surrounded by graphite felt packing. The outer shell ofstainless steel serves as the anode current collector. The cell has abottom inlet line and a top outlet line. Molten sodium acts as thecathode current contact. Molten sodium tetrasullide is fed through thebottom inlet line and sodium pentasulde product is withdrawn through thetop outlet line just below the sodium reservoir. Since molten sodiumacts as the cathode surface, it is necessary to load sodium in thebeta-alumina tube prior to startup.

(F) Pyrolysis of sodium pentasulfide (NazSz) (sulfur recovery): Theapparatus for this step consists of a roundbottom Pyrex ask tted with anitrogen inlet tube, temperature indicator probe and an outlet lineconnected to a chilled receiver and vacuum pump.

In a proposed run, sodium pentasulde is charged to the ask and broughtto the desired temperature and pressure. A slow nitrogen bleed into themelt is used to regulate the vacuum and to provide stirring. Sulfurvapor swept from the flask is collected in the chilled receiver. Thepyrolysis rate and depth of pyrolysis, i.e., approach to Na2S4, can beincreased by raising the temperature and/or lowering the pressure.

(G) Salt analyses: The tot-al analysis of sodium sulfide mixtures wasbased on the procedure outlined in Scotts Standard Methods of ChemicalAnalysis, 5th edition (1939), vol. 2, pp. 2181-2187. The procedure doesnot differentiate between the various polysuldes; therefore.

13 polysulfide samples were always analyzed for total sodium and totalsulfur content to establish the probable molecular formula.

(H) Oil product analyses: Sodium-treated oil products were analyzed notonly for sulfur content, but also for changes in metals content andgeneral physical properties such as API gravity, viscosity andasphaltene content. The oil product obtained from each recovery schemewas filtered hot through a number 2 grade Whatman paper prior toanalysis. Also a sample of the filtered oil was always relluxed intoluene with a small amount of acetic acid to decompose any salts thatescaped filtration and particularly oil soluble salts such as the sodiummercaptides.

Hydrogen sulfide was liberated from any Na2S or NaSH that escapedfiltration. The salt product from this step was sodium acetate which wasfiltered from solution. Finally, desulfurized oil was recovered bydistillation. The acetic acid-treated sample was used as a control toestablish the effectiveness of the salt recovery procedure beingevaluated, i.e., to determine how much sodium (in the form of the salt)was left in the oil after extraction. Also, it was the practice tosample the sodium-treated oil prior to testing a salt recovery schemeand removing the salts by decomposing with acetic acid. This allowed acomparison of the properties of desulfurized oil both before and afterthe particular salt recovery procedure being evaluated.

(I) Sulfur-containing feedstocks: This invention has been demonstratedwith several different sulfur-containing feedstocks. These include boththe 650+ F. and 1030+ fractions of the Bachequero and Tia Juana crudesfrom South America and also the Kuwait Vand Safaniya crudes from theMiddle East. Examples hereinbelow however, are all based on the 650+ F.Safaniya fraction, which is considered to be typical of the residuumfeeds to be encountered commercially. 'I'he properties of this feed arenoted below.

INSPECTIONS OF SAFANIYA ATMOSPHERIC The data below relate to RecoveryScheme A of the specification in which hydrogen sulfide is used toinduce agglomeration of the microcrystalline salts.

To the product mixture obtained from contacting 391 yg. (contains 0.476g.atom sulfur) Safaniya Atmospheric Residuum with 24.8 g. (1.07 g.atom)sodium at 650 F. under 150 p.s.i.g. hydrogen, there was added 7.7 g.(0.23 mole) of hydrogen sulfide. The addition was made at 650 F. withstirring. The HZS reacted instantly and no measurable increase inreactor pressure was noted. The amount of HgS added constitutedapproximately 35 mole percent based on the total moles of salts presentin the oil. The reactor temperature was raised to 685 F. for a 5 minutestirred contact time to insure that NaSH produced by H2S treating wouldmelt. The temperature was then dropped back to room temperature.

Desulfurized oil was decanted from the bomb, leaving a slurry ofprecipitated salts. The salts were subsequently washed with toluene toremove adhering oil and then dried under vacuum. There was recovered40.5 g.

TABLE 1 Analysis of precipitated salt Component: Mole percent N32C03Nagsg Na2S 60.80 NaSH 36.90 NaOH 0.00

N212S03 Na2S203 Nazsolf,

Conversion to the NazS.,= compound was accomplished by blending 20 g. ofthe salt with 176 g. (0.855 mole) of sodium pentasulfide and heating themixture is a stirred flask at 600 F. for 30 minutes. Hydrogen sulfideevolution began when the first signs of melting lwere noted at above 500F. and was complete when the sample became a homogeneous melt at 600 F.The hydrogen sulfide evolved was collected in dilute sodium hydroxidesolution which subsequently was analyzed for sulfide content. The valuedetermined was equivalent to 0.05 mole of HZS or about 92% of thetheoretical amount expected.

Analysis of salt product, Table 2, showed a residual NaSH content ofless than 2 mole percent and a reduction of sodium carbonate to lessthan 0.5 mole percent. The analytical procedure does not differentiatebetween the various polysuliides, hence the notation NagSR. Sodium andsulfur analysis, however, closely checked the theoretical Values for thedesired Na2S4 product.

TABLE 2 Converted salt analyses 1 1 Sample analyzed for 27.1 wt. percentNa and 73.1% sulfur. Theoretical for Naast is 26.4 Wt. percent Na, and73.6 wt. percent sulfur.

It is assumed that a somewhat more stringent treat with Na2S5 willentirely eliminate residual NaSH, thereby providing an exceptionallypure Na2S4 melt for the electrolytic regeneration of sodium. Thecarbonate impurity is deemed to be at sufficiently low concentration notto cause trouble with electrolysis. The carbonate concentration Would becontrolled by taking a purge stream from the molten salt feed toelectrolysis.

Desulfurized oil decanted from the salt slurry was combined with oilrecovered from the toluene wash used in salt purification and wasfiltered hot F.) through number 2 grade Whatman paper to removesuspended salts. The sample was then split into two parts, one fordirect analysis and the other for treatment with acetic acid, todecompose any submicron sodium salts or oil soluble sodium salts such asmight be contained as sodium mercaptides (NaSR). Upon filtration of theacid-treated sample, there was obtained a small amount of sodium acetatewhich corresponded roughly to the difference in oil sodium contents ofthe untreated and acid treated samples (Table 3).

The data indicate that about 650 p.p.m. sodium remains in the oil aftersodium salt recovery via Scheme A, but that it can be reduced to a levelof 50 p.p.m. by treatment with acid. Also the increase in API gravityand drop in asphaltene content shows that the reaction has actuallyimproved the quality of the oil.

TABLE 3.-DESULFURIZED SALT ANALYSES Desulfun'zed oil (Feed) FilteredAcid treated This example relates to Recovery Scheme C of thespecification in which the desulfurizatiou salts are removed from theoil as a molten phase of sodium hydrosulfide. In this example thedesulfurization reaction was carried out with sodium alone.

In the desulfurization reaction 403.5 g. (contains 0.492 g.atom sulfur)of Safaniya Atmospheric Residuum was contacted with 28.1 g. (1.22g.-atom) sodium under an atmosphere of nitrogen for one hour at 650 F.Approximately 34 g. (1.0 mole) of hydrogen sulfide, about 2O molepercent in excess, was injected into the reactor, thereby increasing thereactor pressure from 80 to 220 p.s.i.g. The reactor temperature wasraised to 685 F., held there for minutes with stirring and then droppedto room temperature without stirring. Excess hydrogen suliide was ushedfrom the reactor prior to opening.

Upon decanting the oil phase, the salts were observed to be plated outon the reactor internal surfaces, particularly on the bottom of thereactor, thus indicating that a molten salt phase had formed at 685 F.In commercial operation the molten layer would be withdrawn continuouslyfrom an appropriately designed settling vessel. The solid salts wereremoved from the reactor, washed with toluene to remove oil and thendried under vacuum. There was recovered 48.5 g. of salt (no attempt atquantitative recovery) which gave the analysis shown below in Table 4.

TABLE 4.-ANALYSIS OF HYD ROGEN SUL- FIDE PREPICITATED SALT Weight Molepercent Component As noted, the treat with excess HZS has eliminated allundesirable by-product salts, with the exception of sodium sulfate andcarbonate. 'Ihe water insoluble fraction is coke, which undoubtedlywould slag on the surface of the NaSH melt in commercial operation.

Conversion to sodium tetrasullide was accomplished by blending g. of thesalt with 117 g. (0.568 mole) of sodium pentasulfide and heating at 600F. for 30 minutes. Evolution of hydrogen sulfide began as soon asmelting was observed, at about 500 F., and was complete when ahomogeneous melt was obtained at 600 F.

The HZS collected (5.75 g.) amounted to about 101% of the theoreticalamount expected. Analysis of the melt, Table 5, shows that a remarkablypure polysultlde product was formed with the only signilicantcontaminate being sodium sulfate. Elemental analysis supports theproposed NagS., formula of the polysulfide product.

1 6 TABLE s Analysis of the polysuliide melt 1 Mole percent Component:(normalized) NaZSR 99.5 Na2CO3 0.3 Nagso 0.2

1 Ielt analyzed for 26.8% Na., 72.2% Si; calculated value for ansa is26.4% Na. 73.6% S.

Inspections made on the recovered oil product are shown in Table 6. Thesodium content of the oil is substantially lower than that of the oilobtained in Example 2. The data suggest that salt recovery by generatingmolten NaSH with excess amounts of H28 is an effective recoveryprocedure. It is noted further that sodium treating is very elective forreducing the sulfur content of the oil without degrading the oilproperties. In this case some improvement in oil properties is noted asmanifested in the higher API gravity value and lower viscosity valut`TABLE (Sr-INSPECTIOgS ON DESULFURIZED 1 Viscosity Sabolt Furol.

EXAMPLE 3 The data lbelow illustrate the results obtained using RecoveryScheme D, which is essentially the same as Scheme C, except that sulfuris substituted for sodium pentasulfide in the NaSH conversion step.

To demonstrate this step, 20 g. of a HzS-treated salt mixture containing96.0 wt. percent (98.30 mole percentnormalized) NaSH was blended with16.9 g. (10.529 g.- atom) of elemental sulfur and then heated at 600 F.for 30 minutes. Hydrogen sulfide evolution began at about 300 F. and wascomplete when a homogeneous melt was obtained at 600 F. There wasrecovered 31 g. of melt which exhibited the analysis given in Table 7below. The elemental analysis on the melt (Footnote 1) shows that thedesired salt, NaZS.,l was obtained.

TABLE 7 for NazSl is Na, 26.4%, S, 73.6%.

It is noted that low pressure hydrogen, e.g., less than about 500p.s.i.g., for example 200 p.s.i.g., may be admitted to thedesulfurization zone, if desired, in order to suppress organo metallicsalt formation during the sodium-contacting step; this desulfurizationembodiment may be used in conjunction with any of Schemes A to D.

What is claimed is:

1. A process for the desulfurization of a sulfur-containing petroleumoil stock comprising contacting said oil stock with a desulfurizationagent comprising an alkali metal or an alloy thereof, at desulfurizationconditions, thereby forming a mixture comprising oil of reduced sulfurcontent containing alkali metal salts dispersed therein and contactingsaid mixture with H28, thereby disengaging a substantial portion of saidalkali metal salts from said oil.

2. The process of claim 1 wherein said mixture is contacted with about10 to about 400 mole percent H2S, based on total moles of salt presentin said mixture.

3. The process of claim 1 wherein said mixture is contacted with H2S ata temperature ranging between about 600 and 800 F. and at a pressureranging between about 25 and 50 p.s.i.g.

4. The process of claim 1 wherein said alkali metal is sodium.

5. The process of claim 2 wherein the desulfurization is conducted at atemperature ranging between about 450 and 750 F. and at a pressureranging between about l0 and 600 p.s.i.g.

6. A process for the desulfurization of a sulfur-containing petroleumoil stock comprising contacting said oil stock with a desulfurizationagent selected from the group consisting of sodium and alloys thereof,at desulfurization conditions, thereby forming a mixture comprising oilcontaining alkali metal salts, contacting at least a portion of saidmixture with H2S thereby forming a mixture comprising an oil phase ofreduced sulfur content and a salt phase, contacting the H2S-treatedmixture with a sulfurrich sodium polysulde thereby forming asulfur-depleted sodium polysulde, and, thereafter using at least aportion of said sulfur-depleted sodium polysulde as an electrolyte in anelectrolytic cell for the production of sodium.

7. The process of claim 6 wherein said sulfur-rich sodium polysulde isNa2S5.

8. The process of claim 6 wherein said electrolytic cell comprises ananodic cavity containing polysuliide anions and a cathodic cavitycontaining sodium metal, said anodic and cathodic cavities separated bya sodium ion-conducting membrane comprising beta-alumina.

9. The process of claim 6 wherein the amount of H2S added to thesodium-treated mixture ranges between about 10 and 80 mole percent basedon total moles of salt present in the mixture.

10. The process of claim 6 wherein said sulfur-rich sodium polysulde isrepresented by the formula Na2Sx where x takes values ranging from about4.0 to 4.9 and said sulfur-depleted sodium polysulde is represented bythe formula Na2Sy where y takes values ranging from about 2.8 to 4.5.

, 11. The process of claim 10 wherein y varies from about 2.8 to 3.5.

12. A process for the desulfurization of a sulfur-containing petroleumoil stock comprising contacting said oil stock with a desulfurizationagent selected from the group consisting of sodium and alloys thereof,at desulfurization conditions, thereby fonming a mixture comprising oilcontaining alkali metal salts, contacting at least a portion of saidmixture with H2S thereby forming a mixture cornprising an oilphase ofreduced sulfur content and a salt phase, then separating said salt phasefrom said oil phase and contacting at least a portion of said salt phasewith a sulfur-rich sodium polysulide thereby forming a sulfurdepletedsodium polysulde, and thereafter using at least a portion of saidsulfur-depleted sodium polysuliide as an electrolyte in an electrolyticcell for the production of sodium metal.

13. The process of claim 12 wherein the amount of H2S added to thesodium-treated mixture ranges between about 10 and 400 mole percent,based on total moles of salt present in said mixture.

14. The process of claim 12 wherein said sulfur-rich sodium polysuliideis represented by the formula Na2Sx where x takes values ranging fromabout 4.0 to 4.9 and said sulfur-depleted sodium polysulfide isrepresented by the formula Na2Sy where y takes values ranging from about2.8 to 4.5.

15. The process of claim 12 wherein said electrolytic cell comprises ananodic cavity containing polysullde anions and a cathodic cavitycontaining sodium metal, said anodic and cathodic cavities separated bya sodium ion-conducting membrane comprising beta-alumina.

16. A process for the desulfurization of a sulfur-containing petroleumoil stock comprising contacting said oil stock with a desulfurizationagent selected from the group consisting of sodium and alloys thereof,at desulfurization conditions, thereby forming a mixture comprising oilcontaining alkali metal salts, contacting at least a portion of saidmixture with H2S thereby forming a mixture comprising an oil phase ofreduced sulfur content and a salt phase, then separating said salt phasefrom said oil phase and contacting at least a portion of said salt phasewith sulfur thereby forming sodium polysulde, and thereafter using atleast a portion of said sodium poly-sulfide as an electrolyte in anelectrolytic cell for the production of sodium metal.

17. The process of claim 16 wherein said electrolytic cell comprises ananodic cavity containing polysulde anions and a cathodic cavitycontaining sodium metal, said anodic and cathodic cavities separated bya sodium ion-conducting membrane comprising beta-alumina.

18. The process of claim 16 wherein the amount of H2S added to thesodium-treated mixture ranges between about and 400 mole percent, basedon total moles of salt present in said mixture.

19. The process of claim 16 wherein said sodium polysulfide isrepresented by the formula Na2Sy where y takes values ranging betweenabout 2.8 and 4.5.

20. The process of claim 16 wherein said oil phase is separated fromsaid salt phase and contacted with an acid comprising dilute sulfuricacid or acetic acid.

21. The process of claim 16 wherein the sodium alloy is sodium-lead.

22. The process of claim 6 wherein said oil phase is separated from saidsalt phase and contacted with an acid comprising dilute sulfuric acid oracetic acid.

23. The process of claim 12 wherein said oil phase is separated fromsaid salt phase and contacted with an acid comprising dilute sulfuricacid or acetic acid.

References Cited UNITED STATES PATENTS 3,367,861 2/ 1968 Aldridge et al208-229 3,093,575 6/ 1963 Kimberln, Ir., et al.

208-208 M 3,565,792 2/ 1971 Haskett 208-208 M 2,020,661 11/ 1935 Schulzet al. 208-230 3,164,545 1/ 1965 Mattox 208-230 3,488,271 5/ 1968 Kummer204-180 3,404,036 10/ 1968 Kummer 136-6 3,468,709 9/ 1969 Kummer 136-63,446,677 5/ 1969 Tennenhouse 136-6 3,475,225 10/1969 Tennenhouse 136-6DELBERT E. GANT Z, Primary Examiner I. M. NELSON, Assistant ExaminerU.S. Cl. X.R.

